German Published Unexamined Patent Application No. DE-OS 43 07 159 (see FIG. 1) describes a fuel injector having a spherical valve-closure member which interacts with a flat valve seat surface. In a design of this type, the engaging surface of the sphere is relatively broad in the seat area This is associated with disadvantageous hydraulic adhesive effects which are especially intensified when working with fuels such as ethanol.
Moreover, a fuel injector is described in German Published Unexamined Patent Application No. DE-OS 36 40 830, the valve needle of which has a sealing edge which interacts with a valve seat surface of a nozzle body. The sealing edge is realized by a transition from a cylindrical section to a tapered, conical section of the valve needle. For the most part, therefore, a linear contact exists between the valve needle, with its sealing edge, and the valve seat surface.
A fuel injector having a similar valve seat area is described in German Patent Application No. 37 10 467. The sealing seat of its valve needle is rounded off, however, so that there is no sharp-edged sealing edge. Thus, the cylindrical section of the valve needle changes continually into the conical section. The rounded off sealing seat leads only to a roughly linear contact, which, of course, is dependent upon the radius of the curvature.